Blurring/feathering edges of photos/images

Thank you so much for taking the time and trouble to respond Jack. Sorry it’s taken me a while to come back to you, but I’ve been working through some of your points. The link to the ‘Laser Everything’ guy was extremely interesting and answered a lot of my conundrums re what the settings actually do!
I’ve only been lasering for about 8-9 weeks, and I bought the machine with a specific business format in mind, so I’ve kind of skipped all the basic stuff and launched into photos! With a lot of trial and error I’ve produced some fab results (if I say so myself! haha) but slate was a tricky one - having worked through some of your suggestions and links I’ve managed to get an extremely decent image on slate now, so thank you so much for that! I’m still struggling with the blur/feather issue. I’ve done the feathering in Adobi Illustrator, but when I import it in to Lightburn, there are two elements. The original image sits on top and is absolutely normal, but behind it is a white box with blurred edges, but I can’t ‘marry’ the two together.
This is the link to the message I was referring to in my first post. They refer to ‘transparencies’ in this, but I can’t find anywhere that suggests you can do this in Lightburn.

If I could master this feathering I’d be one very happy lady indeed!! So if you have any further thoughts, please let me know.